Rushed from the courtroom by police officers as she was racked with sobbing after she was cleared by the court, Amanda Knox was taken back to Capanne jail near Perugia and officially released with a speed that took her lawyers by surprise.

Waiting for her in jail was Rocco Girlanda, an Italian MP who has campaigned for her release and who said Knox and her family would spend the night in Rome before taking a scheduled flight back to Seattle on Tuesday.

"She was beside herself with joy and there was a huge cheer when she returned to the prison, an ovation from every cell," he told journalists outside the jail minutes after Knox had sped off into the night in a black Mercedes laid on by Girlanda, on her way to meet her parents at an undisclosed location before driving to Rome.

"Everyone was shouting 'Libera, libera.' It was like being in a football stadium and was something I will never forget. Amanda saluted the other prisoners with a timid wave – she didn't really know how to react."

Knox took minutes to pack up her belongings before thanking the prison chaplain, Father Saulo Scarabattoli, with whom she had spent most of Monday between her final speech and her return to court to hear the sentence.

"She spent the day in the chapel singing then pacing up and down to pass the time as the expected time for the verdict slipped," said Girlanda. "She was nervously asking 'Why do they need so much time?'" he added.

"After the verdict I asked her 'So what really did happen that night?' and she said exactly the same thing she has always said – 'I was at home with Raffaele'. Now the first thing she wants to do is stretch out on green grass," he said.

Earlier in the day Knox's voice had choked with emotion – at times, to the point she was unable to continue until she had caught her breath – as she pleaded with the judges who cleared her and her Italian former boyfriend, Raffaele Sollecito, of the murder of Meredith Kercher.

"I want to go home to my life," she told the court. "I don't want to be deprived of my life, my future, for something I have not done."

At the end of an intensely emotional plea, delivered entirely without notes and in near-perfect Italian, she said very quietly: "Do justice."

On Tuesday night, her request was answered. After a brief statement amid extraordinarily tense courtroom scenes, Knox and Sollecito were cleared of murder. The pair were free to go.

Speaking above the roar of a crowd outside the court in Perugia, Deanna Knox, Amanda's sister, said: "We're thankful that Amanda's nightmare is over. She has suffered for four years for a crime that she did not commit." Deanna also thanked her sister's legal team. "Not only did they defend her brilliantly, but they also loved her," she said.

"We are thankful for all the support we have received – people who took the time to research the case and could see that Amanda and Raffaele were innocent. And last, we are thankful to the court for having the courage to look for the truth and to overturn this conviction."

Knox's lawyer, Carlo dalla Vedova, expressed his condolences to the Kercher family. Asked what Knox would do now, he said: "We're looking forward to taking her back home as soon as possible."

Dalla Vedova told the BBC: "Justice has superseded and has rectified a mistake. It was a terrible tragedy at the beginning because of the death of Meredith.

"Meredith was a friend of Amanda, so we should never forget this. We have to respect the sorrow of the family. But there's no winner here. Justice has recognised that Amanda was not involved in the murder."

Luciano Ghirga, who also represented Knox, called the trial "the case of my life", while Francesco Sollecito, the father of Raffaele Sollecito, said he had "allowed himself some tears" after his son's acquittal.

Speaking outside the court, he said Raffaele had "nothing to do with the death of Meredith Kercher".

He added: "I would have liked to talk to her relatives as well, as they have lost a daughter in a very cruel way. But tonight, they have given me back my son."

As the verdict announced in the courtroom in Perugia was broadcast around the world, there were cries of "She's free!" and "we did it!" in a packed hotel room in downtown Seattle where a group of Knox's friends and supporters had gathered for hours to await the news.

People cheered and hugged as if they had just won the Super Bowl. Tom Wright, a screenwriter and friend of the Knox family, said: "To Amanda herself, we say, way to go kid. We will welcome you with open arms and open hearts."

John Lange, who taught Knox's high school drama class at Seattle preparatory school, wiped away tears with a tissue.

"It's all good, I'm hugely relieved," Lange said, describing Knox, who attended the school for four years before graduating in 2005, as sweet.

"When I knew her she was kind, hard-working and a team player. There was not a mean bone in her body," he said.

In contrast, Kercher's family appeared dazed as the judgment was read out.

They consoled each as Sollecito's relatives punched the air inches away from them in the hot courtroom, which was packed with plain clothes policemen.

Chief prosecutor Giuliano Mignini, removed and folded his court room robes and left without commenting. Outside the court room in a packed piazza lit by television lights, there were shouts of "shame, shame" among the crowd.

"She was there at the scene of crime, how can they just reduce her sentence from 26 years to zero?," asked student Filomena Orlando, 23, who was in the crowd.

Before the verdicts, at a hastily arranged press conference in Perugia, Kercher's family said the "brutal death" of the British student had been overlooked. "I think Meredith has been hugely forgotten," said Kercher's sister, Stephanie, sitting alongside her mother Arline and brother Lyle.

"Everyone needs to remember the brutality of what happened and everything she went through, the fear and the terror, and not knowing why."

"It is very hard to find forgiveness at this time," said Lyle Kercher. "Four years is a very long time but on the other hand it is still raw. You would find it hard to forgive if that was your sibling."

Stephanie Kercher also suggested then that the family would accept the court's decision if it were to overturn them.

"If they decide on the information available to them and not on media hype, justice will be hopefully be done," she said. "Whichever way that will be, we will have to deal with."

Asked if she would reach out to the Knox family, Arline Kercher said: "I don't know. We need to find out what happened."

Meredith's death had left a "huge absence" for the Kerchers, said her brother. "It is as if she went on an extended break and we haven't seen her come back as yet," he said.

Knox had spent the morning in court making her final plea to the court. Standing in a packed but hushed courtroom, her hands raised with her fingertips touching, almost as if in prayer, the 24-year-old said: "I am not what they say [I am]. And I did not do the things they said I did. I didn't kill. I didn't rape. I didn't rob."

Dressed in a green shirt, and black hooded jacket, the University of Washington student – who had been jailed for 26 years for the murder – said she had good relations with all her three flatmates, even if she was a bit untidy and inattentive.

"I lived my life above all with Meredith. She was my friend. She was always kind to me," she said.

Kercher's death had made her frightened and disbelieving, she said; the person "who had the bedroom next to me was killed. And if I had been there that evening, I would be dead. Like her. The only difference is that I was not there. I was with Raffaele."

Earlier, her former boyfriend had made an appeal for his own freedom. "I've never done anyone any harm. Never. In my whole life," Sollecito told the court. He said he had thought the accusation would somehow evaporate. "Instead of which, it's not been like that. I've had to put up with, go on in, a nightmare," he said.

He had spent more than 1,400 days in prison during which, like Knox, he had been confined "for almost 20 hours [a day] in a space measuring two-and-a-half metres by three". He ended by asking to give the judges a bracelet, inscribed with the words "Free Amanda and Raffaele", which he said he had not taken off since the day it was given to him, and which had yellowed with age in the meantime.

It was, he said, "a concentrate of various emotions: desire for justice, and the effort, the path we have followed in this dark tunnel towards a light that seemed ever further away".